Rebuilt the engine and renewed all bearings, seals and piston rings. I then foolishly adjusted the powervalve to the unrestricted position, resulting in having to thrash the engine to get it to move, and blew a piston ring.

General Comments:

The TZR125 is a good looking machine. If kept standard, the engines last a long time and give years of fuss free ownership. The UK model also has the powervalve (YPVS) engine, but powervalve is pegged in restricted position and thus can't operate.

In restricted form, the engine pulls well low down in all gears and has excellent spread of torque. However, turning the powervalve 180 degrees to derestrict the engine, I would not recommend. Reason being, you will have no low-end or mid-range power and a pathetic power band at between 8000 RPM and 10000 RPM.

Fitting the appropriate powervalve servo will alow the best of both worlds. The engine will pull well, just as in restricted form, and then still give mental power at 8000 RPM.

The TZR engine share a lot of its roots with the RD125LC. These engines are reliable and have plenty of tuning potential.

The TZR handles and brakes well and is comfortable even on a long ride. In restricted form it is able to cruise at 60 MPH on the motorway easily. Fuel economy wise you should see figures well into the fifties.

Top speed in restricted form will be about 75mph, and unrestricted models should see 90 mph when standard. Tuned ones will hit the magical ton and beyond, but will last a lot less.

Parts are not as expensive as one might assume, and are easily available as it was a popular bike. There are also many pattern parts available. A lot of two-strokes tend to have nickel coating on the bore, which makes a rebore impossible. The TZR doesn't have this arrangement allowing for rebores if necessary, thus being less expensive should you need to rectify a worn engine.

27th Nov 2016, 21:25

I have a 1989 TZR 125 that is derestricted and it hits 95+ with the powerband kicking in at 7000RPM, but f*** all below that. I also find there is a restrictor at 10500 RPM which stops the engine from revving any higher. Before it was derestricted it hit 80mph with power band at 5000 RPM. I'm currently getting 52 MPG out of it :)